576 Wm. S. Marshall, 



an appreciable difference in the development of the wing rudiment, 

 in fact larvae from 8 mm to 9 mm in length were found in which 

 the wing rudiments were no further advanced than in some larvae 

 onlv 5 mm long : it is also evident that larvae of the same length 

 would necessarily be of different ages depending upon the length of 

 time which had elapsed since the last ecdysis. While a considerable 

 Variation in the stage of development of the wing rudiment in larvae 

 of the same length is noticeable it was found that the longer larvae 

 often showed a less amount of development in this respect than some- 

 what shorter ones. 



An examination of a series of transverse sections of a very young 

 larva shows that at each side in both the meso- and metathoracic 

 Segments there is a pocket fornied by a bulging out of the cuticular 

 and hypodermal layers. Dorsally both of these layers pass gradually 

 over into the pocket without an appreciable boundary between the 

 two although the beginning of the pocket is well defined by the attach- 

 ment of a narrow muscle (Fig. 6, near D). From this point, the dorsal 

 boundary of the pocket, the wall of the body descends with a slight 

 outward slope, this before long changes to a slightly inward direction 

 which finally assumes a dorsal trend; this gives to the pocket a rounded 

 bottom. There next comes a sudden turn back to the first direction, 

 a little outward and ventral, making an acute angle ; at the position of 

 this sudden turn the cuticular layer is thickened, and on to this thicken- 

 ing the muscle just mentioned is inserted. This muscle thus marks 

 the inner boundary of the pocket and between it and the outer wall 

 a small fat body is always found (Figs. 1 und 6, Ft). 



In the older larvae the wing rudiments are easily seen; they are 

 always found on the outer wall of the pocket and in the same trans- 

 verse sections that contain the fat body just mentioned — knowing this 

 it was not difficult to find, in very young larvae, just where each rudi- 

 ment should be, if present. In this position there was always found, 

 as already mentioned, a small darkened area of the cuticula. Kküger (5) 

 found in the larva of Tenebrio molitor that the position of the wing 

 rudiment was shown in an external view by slightly sunken areas 

 covered with light yellow cuticula which was thickened to protect 

 the rudiment of the wing. This same area he found on the prothorax 

 but here it was not so distinct as on the two wing bearing segments 

 of the thorax. Krüger also notes the presence of pigment in the 

 cuticula forming these areas. Tower (16) speaks of wing disks of 

 Lepidoptera lying, shortly before hatching, beneath spots of dark 



